1) Field of the Invention
The field of this invention relates to construction of manually operated vehicles and more particularly to the construction of a bicycle frame which is strong and light in weight.
2) Description of Prior Art
Historically bicycle frames have been constructed of an assemblege of metal tubes. Every bicycle has a front wheel and a rear wheel. Supporting the rear wheel are a pair of what has been called chain stays which extend from a bracket which is used to rotationally support the pedal assembly. From this bracket there is connected a down tube which at its outer end is fixedly secured to a the steering tube which directly connects to a fork which supports the front wheel. From the bracket there also extends substantially vertically a seat tube, the upper end of which has mounted thereon a seat. From the upper end of the seat tube there is a top tube which connects to the steering tube and seat stays which connect to the outer ends of the chain stays. The typical frame of a bicycle thereby is composed of five separate tubular members excluding the steering tube.
Bicycles are used extensively in racing. Also bicycles are commonly used by the public both off-road and on-road. It has always been a particular advantage to construct the bicycle to be as light in weight as possible while maintaining sufficient strength to remain intact and not fail during extended usage of the bicycle over a period of years. The operation of any bicycle inherently receives a series of repetitive shocks. The bicycle frame has to be constructed to not fail from the onslaught of such shocks.
Previously, in order to have the bicycle frame to be of sufficient strength, the bicycle frame was constructed of metal. To make the bicycle frame lighter, the metal was formed into tubes and as previously mentioned there are five such tubes arranged which generally comprise the bicycle frame. In the past it was common to construct such bicycle frames of steel. Although steel frames are definitely of sufficient strength, the steel frame has a weight that is greater than desired.
In order to overcome the inherent disadvantage of steel bicycle frames, there has been developed numerous alloys of metal from which bicycle frames have been constructed. It is been common to construct bicycle frames of titanium alloys with titanium being a strong metal but light in weight. The main disadvantage to the use of titanium is that it is expensive.
It has been found that high strength bicycle frames can be obtained using composite structures which are constructed of carbon, boron, aramid and other synthetic non-metallic fibers bound together with a synthetic liquid resin such as epoxy. A bicycle frame can be made of such materials with a wall thickness which is quite thin and which produces a high strength bicycle frame which is low in weight. With the weight of the bicycle frame being substantially reduced, the overall weight of the bicycle is reduced, which not only enhances competitiveness in operation of the bicycle in racing, it also makes for easier operation for the normal user both on-road and off-road.
Making of bicycle frames out of composite materials in the pas has generally worked with the basic design shape of the bicycle frame, that is the aforementioned five tube arrangement. Composite bicycle frames have been defined in U.S. Pat. No. 4,900,048 inventor Gleb Derujinsky; U.S. Pat. No. 4,657,795, inventor Regis Foret; and U.S. Pat. No. 5,019,312, inventor Stephen J. Bishop wherein the construction of composite bicycle frames is clearly shown utilizing this basic shape of bicycle frame.
However, a variance in the basic shape of a bicycle frame constructed of composite materials is shown and taught within U.S Pat. No. 4,923,203, inventor Brent J. Trimble et al. The shape of the bicycle frame of Trimble et al. is that of an x-shape when viewed from the side. The advantage of this x-shape is that the down tube and the top tube have been combined into one main forward member. Also, the chain stays and the seat stay are in essence combined into one rearward member. The eliminating of members inherently lightens the weight of the bicycle frame which is a most desirable feature. However, the present inventor has found that this x-shape configuration can be significantly improved upon not only acheiving the desired lightening of the construction but also producing increased shock absorbing capabilities within the bicycle frame that are not attained within the x-shape frame of Trimble et al.